The invention is concerned with an automatic firearm and in particular relates to the cartridge chamber of such firearms which have an intensified inertia breech mechanism and, in the cartridge chamber, are provived with a conical transition between bullet chamber and powder chamber, said transition portion serving as a stop means for the cartridge.
In all types of automatic firearms, gas pressure balance grooves permit an increase of the fire cadence and simultaneously the operation of the weapon will become substantially independent of the material quality of the cartridge, and dirty ammunition will not interfere with the firearm function.
In any case the number of such grooves and the length and width thereof will determine the abutment surface which remains in the cartridge chamber and on which the cartridge will be supported during the gas pressure development. Once the bullet has left the cartridge, a pressure balance will occur via said grooves. The bonding of the cartridge at the support surfaces and the finish of the latter determine the slide resistance of the cartridge in the weapon chamber, and this applies in particular to firearms having an intensified inertia breech mechanism.
For ammunition having a shoulder and cartridge neck, the possible maximum number of gas pressure balance grooves is, in known firearms, dependent upon the minimum diameter of the cartridge chamber which is here and in the following referred to as "bullet chamber."